Recently, environmental concern such as reduction of carbon-dioxide emissions has been societal demand. In particular, developing automobiles being fuel-efficient has been increasingly demanded. In the circumstance, it has been desired to develop a material having low rolling-resistance as a material for automobile tires, in particular, for tire tread, which is in contact with the ground surface.
In contrast, from the viewpoint of safety, developing a material having excellent wet skid resistance, and sufficient abrasion resistance and breaking properties in practice has been demanded.
Conventionally, as a reinforcing filler for tire tread, e.g., carbon black and silica have been used.
Use of silica is advantageous since low hysteresis loss property and wet skid resistance can be improved. However, the surface of silica is hydrophilic although the surface of carbon black is hydrophobic. Because of this, silica has drawbacks of low affinity for a conjugated diene rubber and low dispersibility, compared to carbon black. To improve dispersibility and bond silica a conjugated diene rubber, it is necessary to separately add e.g., a silane coupling agent.
Moreover, recently, an attempt has been made to improve dispersibility of silica in a rubber-like polymer by introducing a functional group having affinity and reactivity to silica to an active end of the rubber-like polymer. A further attempt has been made to reduce hysteresis loss by ending a modified end of a polymer by binding of a silica particle.
For example, Patent Literature 1 proposes a modified diene rubber obtained by reacting a modifier having a glycidylamino group with an active end of a polymer.
Patent Literatures 2 to 4 propose a modified diene rubber obtained by reacting an alkoxysilane containing an amino group with an active end of a polymer, and a composition containing the modified diene rubber and silica.
Patent Literature 5 proposes a modified diene rubber functionalized by reacting a cyclic azasilane compound with an active end of a polymer.
Patent Literature 6 proposes a modified diene rubber obtained by coupling an active end of a polymer with a multifunctional silane compound.
In the meantime, it is known that hysteresis loss can be reduced by introducing an amino group having affinity for carbon black into a polymerization initiation end of a rubber like polymer to trap the polymerization initiation end, which is mobile, on carbon black.
Moreover, Patent Literature 7 reports combination of these conventional techniques, more specifically, reports a technique for further reducing hysteresis loss of a modified rubber-like polymer composition obtained from a modified rubber-like polymer, by introducing an amino group having affinity for carbon black into the polymerization initiation end of a rubber-like polymer and introducing an alkoxysilane having an amino group into the polymerization termination end to trap the two terminals with silica and carbon black, respectively.